The invention pertains to an injection-molded plastic part consisting of a first thermoplastic component and a second thermoplastic component. Areas of the first thermoplastic component are present on a surface of the injection-molded plastic part next to areas of the second thermoplastic component. The first thermoplastic component is an LCP. In addition, the invention also pertains to a process for producing an injection molded part using syndiotactic polystyrene.
DE-OS 4,432,966 A1, which also refers to DE 4,416,986 A1, describes a two-component injection-molding process for the production of injection-molded plastic parts of the general type in question and also describes components of this type. In the process, a molded body is injection-molded out of two different thermoplastic components, so that, upon completion of the injection-molding process, the surface of the body consists of adjacent areas of each of these two components. The thermoplastic components used differ with respect to the ease with which they can be metallized. Components which can be metallized include polyamides of the group PA 6, PA 6.6, or PA 6.6/6; acrylonitrile-butadiene-styrene (ABS); polyoxymethylene (POM); liquid crystal polymers (LCP); polyetherimide (PEI); polyethersulfone (PES); polypropylene (PP); and polycarbonate (PC). Glass fibers can be added to the plastic. Components which are disclosed as being unmetallized or metallizable only with difficulty include especially polymers with a high resistance to chemical pretreatment. Here polyamides of the group PA 6, PA 66, carbon black-filled types of PA, PA 11, PA 12, and types of PPA and PA with a filler content of  greater than 50% are used. After the injection-molding process, the part is subjected to a chemical pretreatment, which attacks or changes the two selected components on the surface of the part to different degrees. Through the use of the different plastic components, therefore, different degrees of roughening or different surface structures are produced. A greater degree of roughening or a greater change in the surface of the metallizable component is desirable, because it improves or increases the adhesion of the metal layer during the following metallizing process. At least part of the thickness of a metal layer is formed by purely chemical deposition in an immersion bath.
From the article xe2x80x9cSelective Metallizing of LCPsxe2x80x9d (in the journal MO [Metalloberflxc3xa4che]), Carl Hanser Verlag, Munich, Vol. 53, No. 3, pp. 20-22, 1999), it is known that LCPs (liquid-crystal polymers) can be metallized to make MID parts (molded interconnect devices). Various production methods for MID parts are described, which are formed out of two different types of plastic, combined into a single part. One of the two types of plastic can be metallized. A type of LCP which shows improved selectivity during metallization of two-component injection-molded parts is also disclosed, which, in addition to a mineral filler content of about 40%, contains approximately 50-100 ppm of palladium as a catalyst for electroless plating. To prepare the palladium-containing LCP for metallizing, it is etched with an alkaline solution and then copper is chemically deposited onto the prepared surface, which is then covered with additional layers.
The object of the present invention is to produce an injection-molded plastic part consisting of a first and a second thermoplastic component, where one of the components can be metallized with high selectivity during a metallization process.
The problem is solved in that the second thermoplastic component is a syndiotactic polystyrene (sPS).
The combination of LCP and sPS is especially advantageous, because they have very similar physical properties with respect to processability and shrinkage during cooling in the injection-molding process. Thus, a firm bond with good contact between the components can be achieved. The chemical properties of the LCP and sPS, however, differ advantageously. Whereas LCP is easily attacked chemically by alkaline solutions, for example, and can then be easily metallized, sPS is highly resistant to attack by alkaline solutions. In this case, it is also possible to use, for example, a fiber-reinforced sPS, such as a glass-fiber reinforced sPS.
A particular advantage of the injection-molded plastic part according to the invention is that, because of the high selectivity of this combination of plastics, the LCP and the sPS can be produced in the form of very thin adjacent paths on the surface of the injection-molded plastic part. In the case of conventional injection-molded plastic parts made from two different types of LCP, for example, the minimum width of the paths which can be used is 250 xcexcm, because paths any narrower that this can no longer be metallized precisely when one of the components is metallized. That is, the metallization bleeds over onto the adjacent component, which is not supposed to be metallized, and thus, in the worst case, short-circuits can be created between the paths. When a combination of sPS and LCP is used, however, paths with a width of only about 200 xcexcm can be used. In consideration of the demand for the greatest possible degree of miniaturization of these types of injection-molded plastic parts and of the paths present on them, an advantageous decrease in width of about 20% is therefore obtained without detriment to the precision of the metalization applied to the LCP.
An LCP which contains xe2x89xa720 ppm to xe2x89xa6500 ppm of palladium as a catalyst can be metallized especially effectively. Fiber-reinforced LCP types or those with a mineral filler are also highly suitable. Glass fibers or even carbon fibers, for example, can be used for the fiber reinforcement.
The surface of the injection-molded plastic part should preferably be subjected to alkaline etching to produce or to increase the metallizability and selectivity of the corresponding type of LCP for the addition of the metal layer. If the injection-molded plastic part is to be used as a circuit carrier, the surface of the injection-molded plastic part will be metallized where the LCP is exposed. Etching the LCP with an alkaline solution such as aqueous sodium hydroxide roughens the surface of the LCP, and, depending on the etching time and the etching temperature, erodes a greater or lesser amount of surface material, whereas the sPS is not eroded or roughened but rather retains its original edges with great precision. The use of 10-15 N sodium hydroxide, an etching temperature of 60-90xc2x0 C., and an etching time of 5-60 minutes is favorable. Thus, the etching treatment can produce rough surfaces and/or xe2x80x9ctrenchesxe2x80x9d in the areas of the surface of the injection-molded plastic part where the LCP is present. At the same time, the edges of the sPS areas on the part remain sharply defined. After the etching treatment, the LCP can be metallized with excellent accuracy, that is, with clear definition looking down at an angle of 90xc2x0 to the LCP surface, in that the rough areas are coated and/or the trenches partially or completely filled with metal. The freshly etched LCP surfaces are preferably chemically metallized with metal first, i.e., by electroless plating.
The LCP is preferably electroless plated first with copper, then the copper is covered with additional metal layers or sequences of layers such as layers of nickel, gold, and tin. These layers or sequences of layers can be deposited either with or without an external source of current.
Vectra(copyright) E820i Pd, a type of LCP from Ticona GmbH, and the syndiotactic polystyrene Xarec(copyright) C 132 from Idemitsu Petrochemical Co. have proven to be especially suitable as a combination of thermoplastic components.
The production of an injection molded plastic art using syndiotactic polystyrene as a first thermoplastic component and of an LCP as a second thermoplastic component according to the invention, where at least areas of the first thermoplastic component are present on the surface of the injection-molded plastic part adjacent to areas of the second thermoplastic component, is ideal, especially when the injection-molded plastic part is a MID part.